1. Field of the Invention
The invention relates to pre-balancing methods and apparatus, and in particular to pre-balancing methods and apparatus useful for domestic and commercial washing machines.
2. Brief Description of the Related Art
The need for balancing of washing machine baskets is well known. In a typical washing machine, upon the completion of the wash cycle, the excess water is extracted from clothes during the so-called spin cycle. During a spin cycle, the clothes held in the wash basket are rotated at high speeds. The excess water, acted upon by the centrifugal forces generated by this spinning, is forced out of the clothes and to the outside of the wash basket, where it forced out through the perforations in the walls of the wash basket and into the drain. An efficient water extraction from the clothes is beneficial as it reduces the drying times for clothes.
The efficiency of the water extraction depends on the spin speeds. It is a well-known fact that the higher the spin speed, the higher the water extraction. It is therefore beneficial to afford high spin speeds in washing machines. However, high spin speeds give rise to high levels of vibration caused by imbalances in the wash basket due to uneven distribution of clothes during spinning. Such imbalances randomly change from one wash to the next and their exact magnitudes and locations relative to wash baskets are not known prior to spinning. The difficulty in dealing with such imbalances is further exacerbated by the fact that as the process of water extraction takes place during the spinning operation, the imbalances change. The problem of imbalance and vibration during spinning is undesirable due to stress and damage to the machine and its various components. Furthermore, excessive vibration during the spinning can adversely affect the efficiency of water extraction, result in unwanted noise, and in some cases, cause damage to the sub-floor.
A number techniques have been proposed to deal with the problem of imbalance in wash baskets. The most commonly used technique relies on attaching heavy counterweights to the outer tub, which houses the rotating wash basket. Such counter-weights are typically made of steel, concrete, or some other heavy material, and are intended to reduce vibration by increasing the weight of the suspended assembly. The main disadvantages of such a technique are the increased weight and cost of the machine, as well as the fact that the rotating components are still subjected to the same damaging stresses due to imbalance.
Various alternate techniques have been proposed that counteract the unknown and changing imbalances in wash baskets of washing machines. These techniques are based on the concept of the so-called automatic balancing. Herein, the balancing is achieved by operably mounting an apparatus on the rotating member, which includes an annular cavity containing a balancing fluid or a plurality of movable masses. As sufficient rotational speeds of the rotating member are reached, the balancing fluid or the movable masses position themselves as to counteract the imbalance of the rotating member. One such apparatus is described in U.S. Pat. No. 4,433,592 (Tatsumi et al.). Tatsumi et al. describe a vertical axis washing machine including a wash basket rotatable about its axis of rotation and operably mounted inside the outer tub. The apparatus further includes an annular groove or a race provided in the top plane of the wash basket containing a plurality of freely movable counterbalancing weights. As the wash basket reaches its spin speed, the counterbalancing weights position themselves as to counteract any imbalances in the wash basket.
A similar type of structure is described in the U.S. Pat. No. 2,984,094 (Balaieff). Balaieff describes a front loading, horizontal axis washing machine assembly having annular races or grooves placed at each end and at the outer periphery of the rotating wash basket and concentric with its axis of rotation. The apparatus further includes pluralities of freely movable balls disposed in each of the annular grooves. During the operation of the rotating member, such balls position themselves so as to compensate for any unbalanced static and dynamic loads.
Another type of apparatus is described in U.S. Pat. No. 5,448,979 (Ryan et al.). Ryan et al. describe a wash basket with two balancing rings including annular grooves partially filled with a balancing fluid, such as water. The annular grooves are placed at the opposite ends of the wash basket. During operation, the balancing fluid flows into the direction so as to counteract the imbalance forces.
Further, a similar structure is described in U.S. Pat. No. 5,345,792 (Farrington et al.). This document describes an apparatus including a plurality of annular grooves disposed at each end of the wash basket and containing pluralities of balancing fluids.
Yet further types of apparatus are described in U.S. Pat. No. 5,850,748 (Kim et al.). Kim et al. describes a wash basket of a front loading horizontal axis washing machine including two concentric annular races placed at each end of the wash basket, each pair of annular races containing compensating weights of different size with the inner races having smaller weights than the outer races.
Such prior devices provide compensation for imbalance at the spin speeds; however, these devices have certain disadvantages. It is well known to those skilled in the art that automatic balancers counteract the imbalance forces in rotating members at speeds which are above the so-called resonant or critical speed of the suspended assembly. In typical washing machines, and indeed in most washing machines, such critical speeds are lower than the design spin speeds of rotation of the wash baskets. Therefore, automatic balancers, such as those described in the above prior documents, are able counteract the imbalances at spin speeds. However, automatic balancers are ineffective for rotating speeds below the critical speeds and actually can add to the imbalance forces. A consequence of this limitation is that during the entire time that the wash basket is accelerated from its initial position of rest to the operating speed, the wash basket remains severely unbalanced. Furthermore, upon start-up, as the speed of rotation approaches the critical speed of the suspended wash assembly, violent resonant oscillations occur resulting in the assembly often hitting the cabinet of the washing machine. In fact, it has been observed that such resonances are often more severe in cases when automatic balancers are deployed. Correspondingly, heavy counterweights must be utilized to control such resonances and on occasion larger washing machine cabinets are required. This, in turn, results in higher cost of the machine, higher transportation costs, and inconvenience to the end user.
Furthermore, most modem machines come equipped with imbalance sensors and/or trip switches to protect the fragile electronic systems. Therein, if sufficiently large imbalances, or excessive vibration levels during start-up, are detected, the washing machine will not begin the spin cycle. As a result, water extraction will not take place until the user manually rearranges the wet laundry inside the wash basket. Herein lies a significant disadvantage of the above prior devices. Since imbalance detection takes place at low speeds, which are below the resonant speeds, greater imbalances will typically be sensed with automatic balancers. Similarly, as the machine accelerates through its resonant speed, higher levels or resonant vibrations will typically result with automatic balancers. Consequently, such systems can be detrimental to the proper engagement of spin cycles.
One solution to overcome the disadvantages of the above prior art is through so-called pre-balancing. It is known to those skilled in the art that some type of pre-balancing of the wash loads is required prior to engaging the spin cycle, regardless of whether the machine is equipped with automatic balancers or not. Pre-balancing refers to a process or a procedure wherein a balanced or partially balanced condition for the wash basket is achieved at low speeds (i.e., below the resonant speeds) of rotation prior to accelerating to desired spin speeds.
Conventional methods of achieving such pre-balancing rely upon a variety of tumbling motions preceding the attempts of engaging the spin cycles. Such tumbling motions are aimed at redistributing the wash load and are often accompanied by periodic additions of water. The disadvantages of such methods are well known to those skilled in the art. Notable among the disadvantages, such methods do not eliminate the need for heavy counter-weights. These prior methods are based on predefined sequences of movements resulting in substantially random changes to the distribution of clothes. Also, since there are no external aids to the pre-balancing process, the process is, in general, unreliable, and hence, the use of heavy counterweights cannot be avoided. Another disadvantage of such methods lies in increased water usage, which creates waste. Yet another disadvantage is associated with occasionally long pre-balancing times before an acceptable level of residual imbalance is sensed.
A different type of method for achieving pre-balancing is described in U.S. Pat. No. 5,862,553 (Haberl et al.). Haberl et al. describes a clothes washing machine apparatus equipped with automatic balancing devices. The balancing devices include a plurality of annular races (hollow members) mounted onto the wash basket (rotating tub), within which races pluralities of freely movable masses are disposed. Additionally, a damping fluid is disposed in each of the hollow members. The apparatus further includes devices which rotate the wash basket at various speeds of rotation and means which sense the acceleration and frequency of rotation. Haberl et al. describes that before at least one spin extraction phase, the drum is rotated at a relatively low speed until the compensating masses position themselves substantially so as to counteract the imbalances of the wash load. Such relatively low speeds are, according to Haberl et al, lower than the resonant speeds of the suspended assembly but sufficiently high to cause the wash load items to adhere to the wash basket.
The apparatus described by Haberl et al. relies primarily on fluctuations in the speed of rotation of the drum over each revolution and the viscous dragging action imparted on the compensating masses by the damping fluid during the low speed rotation. Haberl et al. describe that the fluctuations in the speed of the drum are caused by a wash load imbalance acted on by the force of gravity. During low speed rotation, as the imbalance mass is carried upward, the rotational speed of the drum decreases from its mean value due to the opposing action of the gravity force. Subsequently, as the imbalance mass is rotated in a downward direction, the gravity force assists in the rotation and the drum accelerates. Similarly, the movement of the compensating masses relative to the rotating drum fluctuates. As the compensating masses are rotated upward from their low position by the dragging action of the viscous fluid, the gravity forces oppose such movement which prevents the compensating masses from moving together with the rotating drum and causes them to fall behind. The compensating masses continue to fall behind in their movement relative to the rotation of the drum until they reach the top position, as which point the force of gravity begins to assist in their movement.
Haberl et al. describes that such fluctuations of the rotating movement of the drum in combination with the fluctuations in the movement of the compensating masses result in the compensating masses positioning themselves substantially in opposition to the wash load imbalance, and thus self-balancing the rotating drum. Haberl et al. indicate that through proper selection of the key parameters, such as the mean speed of rotation and the viscosity of the fluid, a self-balancing action for the rotating drum can be achieved at low speeds of rotation through the interaction of the above-described motions.
The apparatus of Haberl et al. has, however, some disadvantages. One of the disadvantages is that the proposed solution takes into account the forces caused by the rotational speed variations of the drum. It has been found experimentally that this is only correct under specific circumstances where, among other things, the movements of the entire suspended assembly during the low speed rotation are sufficiently small so as not to impact the desired variations of the aforementioned motion for the rotating drum and compensation masses.
Yet another disadvantage of the device of Haberl et al. lies in the fact that the key parameters, i.e., mean speed and viscosity of the damping fluid, are chosen to provide the optimum performance for some predefined and anticipated typical imbalance condition. Since in actual operation the imbalance condition will vary and, with it, the fluctuations in the rotating velocity of the drum, self-balancing performance will generally deviate from the optimal. Additionally, depending on the particular wash cycle (which is not known in advance), the temperature of the damping fluid will vary. This will affect the fluid""s viscosity, which in turn will cause the movement of compensating masses to deviate from the desired one. In all, such variations in operating conditions will negatively impact the self-balancing action of the rotating drum.
Yet a further disadvantage of the above prior approaches originates from the fact that the low speed balancing (self-balancing) is performed above stick-speeds, i.e., speeds which are sufficiently high to ensure the wash load adheres to the wash basket at all times. It has been found experimentally that on most domestic and commercial machines stick speeds are too high for quick, accurate, and reliable self-balancing action. Moreover, such stick speeds are high enough to cause considerable movements in the suspended assembly due to rotating motion of the wash basket, which in turn, further impacts the self-balancing action.
It has also been found that the above disadvantages often result in long pre-balancing times, i.e., time intervals required to achieve sufficiently good balance of the wash basket. Long pre-balancing times, however, give rise to the onset of unwanted xe2x80x9cdynamic imbalancesxe2x80x9d which originate within the balancers themselves. This is particularly true when the amount of actual imbalance is considerably lower than the balancing capacity of the balancers. Herein, although in a static sense, the balancers at either end of the wash basket substantially counteract the wash load imbalance, the compensating masses in the two units, or certain amounts thereof, are in effect opposite to each other. This gives rise to dynamic imbalance (or the so-called imbalance couple) and causes violent resonant rocking mode vibration when the wash basket is accelerated during the spin extraction phase.
A structure and a method similar to those in Haberl et al, is described in SE 9803567-8. However, most of disadvantages of the Haberl devices are also present in this latter disclosure.
One aspect of the present invention relates to a method for reducing an out-of-balance condition during the low speed rotation of the wash basket of a laundry clothes washing machine, the machine including a cabinet frame, an outer tub, springs and dampers resiliently supporting the outer tub in the cabinet frame, a wash basket rotatably positioned inside the outer tub and capable of rotating about an axis of rotation, and means for rotating the wash basket at different speeds of rotation about the axis of rotation, two automatic balancers attached to the wash basket at each end of the wash basket, the automatic balancers having an axis of rotation substantially coincident with the axis of rotation of the wash basket, means for detecting a condition indicative of imbalance of a load in the wash basket at low speeds of rotation, the method comprising the steps of accelerating the wash basket to first speed of rotation, said first speed of rotation being below a resonant speed of the supported assembly of the washing machine and higher than a speed at which any wash load movements inside the wash basket occur, decelerating from the first speed of rotation to a second speed of rotation, the second speed of rotation being lower than the first speed of rotation, the second speed of rotation being sufficiently low to initiate the movement of the wash load in the wash basket, and continuing the wash basket rotation at speeds lower than the second speed of rotation until movements of the wash load and the action of the automatic balancers impart a dynamic balancing condition which reduces the out-of-balance condition of the rotating wash basket below a predetermined level.
Another aspect of the present invention relates to a washing machine useful for reducing an out-of-balance condition thereof, the machine comprising a cabinet frame, an outer tub, springs and dampers resiliently supporting the outer tub in the cabinet frame, a wash basket rotatably positioned inside the outer tub and capable of rotating about an axis of rotation, two automatic balancers attached to the wash basket at each end of the wash basket, the automatic balancers having an axis of rotation substantially coincident with the axis of rotation of the wash basket, means for detecting a condition indicative of imbalance of a load in the wash basket at low speeds of rotation, and means for controlling the velocity of the wash basket including means for rotating the wash basket at different speeds of rotation about the axis of rotation, logic for accelerating the wash basket to first speed of rotation, said first speed of rotation being below a resonant speed of the supported assembly of the washing machine and higher than a speed at which any wash load movements inside the wash basket occur, logic for decelerating from the first speed of rotation to a second speed of rotation, the second speed of rotation being lower than the first speed of rotation, the second speed of rotation being sufficiently low to initiate the movement of the wash load in the wash basket, and logic for continuing the wash basket rotation at speeds lower than the second speed of rotation until movements of the wash load and the action of the automatic balancers impart a dynamic balancing condition which reduces the out-of-balance condition of the rotating wash basket below a predetermined level.
Yet another aspect of the present invention relates to a method for reducing an out-of-balance condition during the low speed rotation of the wash basket of a laundry clothes washing machine, the machine including a cabinet frame, an outer tub, springs and dampers resiliently supporting the outer tub in the cabinet frame, a wash basket rotatably positioned inside the outer tub and capable of rotating about an axis of rotation, and means for rotating the wash basket at different speeds of rotation about the axis of rotation, two automatic balancers attached to the wash basket at each end of the wash basket, the automatic balancers having an axis of rotation substantially coincident with the axis of rotation of the wash basket, means for detecting a condition indicative of imbalance of a load in the wash basket at low speeds of rotation, the method comprising the steps of accelerating the wash basket to first speed of rotation, said first speed of rotation being below a resonant speed of the supported assembly of the washing machine and lower than a speed at which no wash load movements inside the wash basket occur, accelerating gradually from the first speed of rotation to a second speed of rotation, the second speed of rotation being higher than the first speed of rotation, the second speed of rotation being sufficiently high so as to prevent any movement of the wash load in the wash basket, and continuing the wash basket rotation at speeds equal to the second speed of rotation until movements of the wash load and the action of the automatic balancers impart a dynamic balancing condition which reduces the out-of-balance condition of the rotating wash basket below a predetermined level.
Yet another aspect of the present invention relates to a washing machine useful for reducing an out-of-balance condition thereof, the machine comprising a cabinet frame, an outer tub, springs and dampers resiliently supporting the outer tub in the cabinet frame, a wash basket rotatably positioned inside the outer tub and capable of rotating about an axis of rotation, two automatic balancers attached to the wash basket at each end of the wash basket, the automatic balancers having an axis of rotation substantially coincident with the axis of rotation of the wash basket, means for detecting a condition indicative of imbalance of a load in the wash basket at low speeds of rotation, and means for controlling the velocity of the wash basket including means for rotating the wash basket at different speeds of rotation about the axis of rotation, logic for accelerating the wash basket to first speed of rotation, said first speed of rotation being below a resonant speed of the supported assembly of the washing machine and lower than a speed at which no wash load movements inside the wash basket occur, logic for gradually accelerating from the first speed of rotation to a second speed of rotation, the second speed of rotation being higher than the first speed of rotation, the second speed of rotation being sufficiently high so as to prevent the movement of the wash load in the wash basket, and logic for continuing the wash basket rotation at speeds equal to the second speed of rotation until movements of the wash load and the action of the automatic balancers impart a dynamic balancing condition which reduces the out-of-balance condition of the rotating wash basket below a predetermined level.
Yet another aspect of the present invention relates to a rigid mode washing machine useful for reducing an out-of-balance condition thereof at low speeds of rotation, the machine comprising a cabinet frame, an outer tub rigidly mounted to the cabinet frame, a wash basket rotatably positioned inside the outer tub and capable of rotating about an axis of rotation, means for detecting a condition indicative of imbalance of a load in the wash basket at low speeds of rotation, and means for controlling the velocity of the wash basket including means for rotating the wash basket at different speeds of rotation about the axis of rotation, logic for accelerating the wash basket to first speed of rotation, said first speed of rotation being lower than a speed at which no wash load movements inside the wash basket occur, logic for gradually accelerating from the first speed of rotation to a second speed of rotation, the second speed of rotation being higher than the first speed of rotation, the second speed of rotation being sufficiently high so as to prevent the movement of the wash load in the wash basket under the condition of no imbalance, and logic for continuing the wash basket rotation at speeds equal to the second speed of rotation until movements of the wash load are no longer present and the out-of-balance condition of the rotating wash basket is below a predetermined level.
Still other objects, features, and attendant advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description of embodiments constructed in accordance therewith, taken in conjunction with the accompanying drawings.